This invention relates to guide rolls for supporting a hot workpiece under elevated temperature conditions, and in particular to continuous caster guide rolls having means to alleviate internal thermal stress caused by both the hot cast strand and ambient temperatures.
In continuous casting operations solidification of the cast molten steel starts in a water cooled mold and continues progressively as the strand moves from the mold, through secondary water spray cooling zones and onto a straightener for further processing. A plurality of guide rolls are arranged to support and guide the hot strand toward the straightener. Guide roll arrangements vary with each different caster design, however, they typically comprise 1) a fixed vertical set of rolls positioned immediately below the caster mold, 2) a set of bend unit rolls positioned to initiate a direction change from vertical strand movement to horizontal strand movement, and 3) a curved rack of guide rolls positioned to guide the strand onto the straightener.
During continuous casting operations radiant heat is emitted from the hot cast strand and causes the guide rolls to expand circumferentially as well as or grow along their longitudinal axis. The extra expanded roll length impacts upon the bearings of the guide roll assembly, generates uneven lateral and radial forces against the bearings, and causes stuck rolls and/or bearing failure. Additionally, from time to time it may be necessary to slow down casting speeds to meet various shop conditions. Under such circumstances the rotational speed of the guide rolls may be reduced to as little as one revolution per every six minutes. At such slower casting speeds temperature differentials along the roll circumference can be raised to as much as 600.degree. F. These temperature differentials are due to one side of the guide roll being positioned adjacent the hot cast strand while the opposite side of the guide roll is being emersed in secondary cooling sprays. The wide temperature differential between opposite sides of the guide roll produces unequal roll growth, bulging, and generates asymmetrical lateral and radial forces against the bearings supporting the guide roll.
The problems and failures described above add unwanted expense to continuous casting operations. Bearing failures require shutdown for maintenance, repair, and replacement of rollers and bearings. And, in extreme instances, stuck rolls rupture the thin solidified skin forming along the hot cast strand and cause a breakout, a dangerous eruption of molten steel spewing from the molten core of the strand.